Chemically-induced genetic damages of cells (mammalian or submammalian) in vitro are observable by allowing the cells to express their DNA damage and the progenies with locus-specific mutation to be selected and form colonies, During FY'84, work has been in progress on: (1) acute toxicity, (2) criteria for classifying assay results into the following categories: positive, negative, equivocal and not classifiable, and (3) statistical methods of data analysis. This work has been based on data of 200 chemical compounds. Reports describing the cell mutation assay and the statistical methods for analyzing the Ames mutation assay have been prepared. All scientific reports should be completed in FY'85.